1. Field of the Invention
This invention relates generally to the generation of heat using eddy currents and more particularly to apparatus and method for generating heat utilizing permanent magnets.
2. Description of the Related Art
Heat can be generated in an electrically-conductive material by subjecting it to a magnetic field, where either the conductive material or the magnetic field is in motion. A varying or moving magnetic field produces eddy currents in a conductive material placed in the magnetic field. A changing magnetic field causes rapid movement of the electrons in the conductive material, which generates heat. The use of electromagnetism in induction heating is a relatively developed art that Unlike induction heating where the magnetic field is generated, the magnetic field is already present an permanent magnet heating. Induction heating typically uses a varying frequency alternating electric current rather than a standard, constant-frequency alternating current (AC) supplied by a utility company. Permanent magnet heating does not require a variable frequency AC electric field.
Permanent magnet heating is attractive because high power densities can be generated directly in the body and/or material to be heated. Thus, it is highly efficient. Variables that effect the amount of heat generated include: the strength of the magnetic field, the number of magnets, the spacing between the permanent magnets, the relative speed between the permanent magnets and the material to be heated. The greater the magnetic field strength the greater the heat generated in an adjacent conductive material. The greater the relative speed the greater the heat generated, as this provides a greater frequency of field change. Other factors that effect the amount of heat generated are the resistivity, permeability, size, and shape of the body to be heated, and magnet size and shape.
The material to be heated is referred to as the conductive material, a solid and/or fluid. Resistivity and permeability vary substantially in conductive materials, which may be classified by their magnetic properties as diamagnetic, paramagnetic, and ferromagnetic materials. Diamagnetic materials oppose the establishment of a magnetic field and include copper, gold, and silver. Paramagnetic materials can be weakly magnetized by a strong magnetic field and include aluminum and platinum. Ferromagnetic materials are easily magnetized by a strong magnetic field and include iron, nickel, steel, some rare earth metals, and alloys thereof. While ferromagnetic materials provide the highest efficiency for induction heating, it is believed that diamagnetic materials provide the highest efficiency for permanent magnet heating because permanent magnets magnetize ferromagnetic material, causing a loss in the strength of the magnetic field of the permanent magnet.
The present invention pertains to a heating apparatus for the heating of a medium with several adjacently arranged permanent magnets which produce a magnetic field inside of which an electrically conducting material is placed. A linear and/or rotating relative motion is produced between the material and the permanent magnets whereby the material is heated.
Swiss patent application CH-PS 662 691 shows a turbo-molecular pump wherein a rotor is arranged in a high-vacuum side of the interior of a housing. Attached to the rotor are discs which cooperate with stator discs fastened to the housing. In order to accelerate the desorption of the high-vacuum side surfaces, the construction parts with these surfaces are heated. To accomplish this, the rotor is heated by eddy currents, which arise from the interaction of the rotor's own rotation with a magnetic field whose field lines run perpendicular to the rotor axis. The magnetic field is produced by a permanent or electro-magnet, fastened outside the housing, the magnetic field lines of which run perpendicular to the rotor axis. With this heating arrangement, only a limited heating capability is possible.
Danish patent application DE-A-1 106 440 shows a rotating bell made of ferromagnetic material arranged at the base of a steam-producing vessel constructed of good conducting material. On the outside surface of this bell, rim-shaped permanent magnets are placed which radiate a magnetic field in an alternating pole fashion. The vessel surrounding the bell has a ring encompassing the magnets at a small distance which is likewise made of ferromagnetic material, for example soft iron. By rotating the bell, the permanent magnets located on its circumference effect a heating of the surrounding vessel and the ring due to the eddy currents which arise. The latter conducts the heat to the water present in the vessel. The heat transferred with this apparatus does not result in optimal heat transfer to the water medium to be heated.
U.S. Pat. No. 4,421,967, issued to Birgel et al. discloses a windmill electric heater that converts wind energy to heat energy. A windmill drives a rotor of an eddy current heater. Magnetic fields are provided at an air gap between the rotor and a stator of the eddy current heater. Rotation of the rotor with respect to the stator causes eddy currents, and therefore heat, to be generated in the rotor. The heat generated in the rotor is drawn off for beneficial use such as in heating a house. Excitation of the magnetic fields (and therefore the amount of heat generated) is controlled as a function of sensed parameters such as wind velocity, ambient temperature of the surroundings to be heated and temperature of the eddy current heater.
U.S. Pat. No. 4,511,777, issued to Gerard, discloses a rotary magnet thermal generator system having an array of magnets in an alternating disposition coaxially disposed about and parallel with the shaft of a motor driving the rotary array and having a copper heat absorber and a ferro-magnetic plate fixed on a face of the heat absorber. The device includes a plurality of heat sink plates extending beyond the ferro-magnet plate into a plenum through a respective plurality of close-fitting apertures.
U.S. Pat. No. 4,614,853, issued to Gerard et al., discloses a magnetic thermal generator that has axially aligned, spaced-apart shafts, each with an electric motor at the outer end and on each inner end a permanent cylindrical magnet rotor with alternate north-pole and south-pole disposition of magnets parallel to each other in a circle about the shaft axis. In the spacing between the inner ends of the shafts a boiler is axially affixed. The boiler is of steel, is cylindrical in cross-sectional shape, and has at each end a steel disk-shaped end closure on the outside of which is bolted a copper disk of the same size. Fixed to the copper disk and extending hermetically through the end closure are a plurality of copper heat sinks, with axially alternative larger and smaller diameters; preferably the copper heat sinks from the respective ends are coaxially disposed and terminate within the boiler adjacent to each other but not touching. A steam dome protrudes from the top of the boiler and water inlet, water vent to the steam dome and steam exhaust are provided for water to be heated and passed transversely through the boiler into the steam dome.
Devices disclosed in the U.S. Pat. Nos. 4,511,777 and 4,614,853 share a similar design and several inefficiencies. In such devices part of the permanent magnets' energy is used to magnetize ferromagnetic material, causing a loss in the permanent magnets' stored energy. A ferromagnetic plate adjacent a plate to be heated, but away from the magnets, weakens the magnets by imparting a dynamic load on the magnets, assuming the magnetic field reaches that far. Further, the thermal design is poor in that the copper plate to be heated is too large, making the thermal mass too large and resulting in wasted heat.
U.S. Pat. No. 5,012,060, issued to Gerard et al. discloses a permanent magnet thermal generator having at least one stationary permanent magnet and a rotatable rotor assembly for producing and absorbing heat from the magnetic flux from the permanent magnet as the rotatable rotor is rotated. The rotor assembly serves as a heat absorber, an impeller to move a heat transfer fluid around the rotor assembly and to transfer heat to the heat transfer fluid that moves around the rotating rotor. In one embodiment the strength of the permanent magnet is varied by adding or subtracting magnets and in another embodiment the rotor assembly is constructed in such manner that the heat transfer fluid is recycled around the rotor assembly. Furnace, steam boiler and refrigeration systems incorporating a permanent magnet thermal generator are also set forth. The device described in this patent has an inefficient magnet configuration and a poor thermal design.
The present invention addresses many problems with the presently known systems and provides permanent magnet heating apparatuses that are efficient and relatively easy to manufacture. Features and characteristics of the present invention include: a shape that links magnetic fields enhancing field strength; a design for holding magnets in place while under rotational forces; a design for a conductive material that enhances heat transfer to a fluid; a design for simultaneously heating and pumping a fluid; and/or a design for avoiding corrosion of magnets. The present invention is useful in a variety of applications.